Bernd Dorn a écrit :

On 06.03.2007, at 18:54, Christophe Combelles wrote:


I'm playing again with the notion of categories of objects.

I have two main goals:
1) I must let the user choose the category of an object added to the zodb. For this, I must be able to retrieve the list of categories and present them in a form field managed by a vocabulary (or in a different manner).
2) I must have different behaviours for categorized objects:
objects of different categories would have different views, different addMenuItems (if they are containers), etc.

the first requirement would tell me to define categories as objects, while the second one would tell me to define them as interfaces.

The possible solutions I see:

1) The simplest solution is to store the categories as text strings into the annotations of the object. So categories actually are just tags.

2) The second solution is to do the same, but replace text strings with category objects, that implement ICategory. And categories can be stored separately in a category container, or in a registered utility that gives the list of available categories. This is a bit better, but this way I don't know how to easily let my categorized objects behave differently according to their categories.

3) The third solution is to define categories as interfaces extending ICategory. I can retrieve the list of categories with ICategory.dependents But to present them in a form, I must have a pretty name for each interface. Should I store them in a Tagged Value?

4) The fourth solution I see, is to define an interface type, ICategoryType, extending IInterface just like IContentType. Then my categories would be interfaces whose type is ICategoryType. But with IContentType, is there a way to retrieve the list of all available content types?

imho 4) is the best solution, just take a look at to see how to get the vocabulary and the inspection implementation of objects

you can then set the interface on objects by using zope.interface.alsoProvides

But with 4), I guess I won't be able to assign two categories onto an object,
An object can have only one ContentType

I feel that 3) is easier, but I don't know how to assign an retrieve a display name to interfaces.

A real example is the following:

I want to define objects that represent Companies.
A company can be either a client, or a provider, or both,
or in the future it could be of another type.

When the user creates a company, it must choose "client", "provider", or both.
The choice would assign a different interface to the object:
IClient, or IProvider, and this would lead to different views for these objects.

So "client" and "provider" are categories of companies.

So I would tend to have:

class ICompany(Interface)

class IClient(ICompany)

class IProvider(ICompany)

This is simple, but now how do I assign a name to these interface, so that the user will choose between "Client" and "Provider", and not between "IClient" and "IProvider"? Is it feasible with Tagged Value ? Or with the "name" attribute in the zope:interface ZCML declaration?

regards, Bernd

Do you have some advice on the subject? Am I asking the wrong questions? Is there an obvious solution I've not seen? Am I going too far and should I rather keep it simple and stupid?


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